2 cups (320 grams) fresh cherries, pitted and roughly chopped
1/2 cup (99 grams) granulated sugar
1 1/2 tablespoon cornstarch
1 tablespoon lemon juice
1/3 cup water
2 3/4 cups (330 grams) all-purpose flour
3 cups (594 grams) granulated sugar
1 cup (84 grams) natural unsweetened cocoa powder
1 tablespoon baking soda
1 1/2 teaspoon baking powder
1 1/2 teaspoon salt
3 large eggs, room temperature
1 1/2 cups (340.5 grams) buttermilk
1 1/2 cups (340.5 grams) hot coffee
3/4 cup (148.5 grams) vegetable oil
1 tablespoons vanilla extract
1 1/2 cups (339 grams) unsalted butter
7-8 cups (795-908 grams) confectioners' sugar
1/2 teaspoon salt
3/4 teaspoon vanilla extract
1 1/2 cups (240 grams) cherries, pitted and finely chopped
Make the cherry filling. Place the cherries, sugar, cornstarch, lemon juice, and water in a large saucepan and bring to a boil. Boil for 5 minutes, stirring frequently, until the cherries soften and the liquid is thick enough to coat the back of a spoon. Set aside to cool; refrigerate while making the rest of the cake.
Make the chocolate cake. Preheat the oven to 350 °F. Grease and flour three 8-inch round cake pans. Line the pans with parchment paper, then grease and flour the parchment paper.
Make the cake batter. Using a mixer, combine together the flour, sugar, cocoa powder, baking soda, baking powder, and salt in a large bowl. In a separate smaller bowl, whisk together the eggs, buttermilk, coffee, oil, and vanilla extract. Add the wet ingredients to the dry ingredients and mix on low speed until combined, about 2 minutes. The batter will be thin.
Bake the cake batter. Divide the batter evenly among the three pans. Bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out with a moist crumb. Cool the cakes in the pan for 20 minutes, then turn them out on cooling racks to cool completely before frosting.
Make the frosting. In the bowl of a stand mixer, beat the butter until light and fluffy, 3 to 4 minutes. Add in the confectioners' sugar, 1/2 cup at a time, up to 7 cups total. Beat in the salt and the vanilla extract, followed by the chopped cherries and any released cherry juice. Turn the mixer to medium-high speed and beat until light and fluffy, 2 to 3 minutes. If the frosting is too thin, add additional confectioners' sugar until the desired texture is achieved.
Assemble the cake. Level the cakes if necessary. Cover the bottom layer of cake with 3/4 cup of the frosting. Pipe a border of frosting along the outer edge of the cake and refrigerate for 10-15 minutes. Spread half the cooled cherry filling inside the piped frosting border. Top with a second cake layer and repeat. Place the final layer on top of the cake, face down, and frost the sides and top of the cake. Refrigerate to set the frosting.